Electrochemical device and electronic device

Abstract

An electrochemical device and an electronic device, the electrochemical device comprises a positive electrode plate, the positive electrode plate comprises a positive electrode material layer, the positive electrode material layer comprises a positive electrode active material, the elements in the positive electrode active material comprise Li, Mn, Ni, Co and Fe, wherein the positive electrode active material satisfies at least one of the following characteristics: (i) the ratio A of the number of Mn atoms to the total number of Ni, Co and Fe atoms is 3.5 to 40; (ii) the ratio B of the number of Li atoms to the total number of Mn, Ni, Co and Fe atoms is 0.51 to 0.79. By regulating the elements in the positive electrode active material to meet the range of A and / or B, it is beneficial to improve the comprehensive performance of the electrochemical device.

Description

Technical Field

[0001] The present application relates to the field of electrochemistry, and in particular to an electrochemical device and an electronic device. Background Art

[0002] Lithium-ion batteries are widely used in wearable devices, smart phones, drones, electric vehicles and large-scale energy storage equipment due to their advantages such as high energy density, long cycle life and no memory effect. They have become the most promising new green chemical power source in the world today, but they also put higher requirements on the comprehensive performance of lithium-ion batteries.

[0003] The performance of lithium-ion batteries mainly depends on the characteristics of the positive electrode, negative electrode, electrolyte and separator. Among them, the active materials in the positive and negative electrodes are one of the important factors affecting the performance of lithium-ion batteries. Ternary layered nickel cobalt lithium manganese oxide, lithium manganese oxide, and lithium iron phosphate are commonly used positive electrode materials and are widely used in the fields of electric vehicles and electric bicycles. However, there are still at least one of the problems of short battery life, poor cycle performance, and poor high and low temperature storage performance. That is, the comprehensive performance of lithium-ion batteries still needs to be improved. Summary of the invention

[0004] The purpose of the present application is to provide an electrochemical device and an electronic device to improve the comprehensive performance of the electrochemical device.

[0005] The first aspect of the present application provides an electrochemical device, which includes a positive electrode plate, the positive electrode plate includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and the elements in the positive electrode active material include Li, Mn, Ni, Co and Fe, wherein the positive electrode active material satisfies at least one of the following characteristics: (i) the ratio A of the number of atoms of Mn to the total number of atoms of Ni, Co and Fe is 3.5 to 40; (ii) the ratio B of the number of atoms of Li to the total number of atoms of Mn, Ni, Co and Fe is 0.51 to 0.79. Without being limited to any theory, by regulating the elements in the positive electrode active material to meet the range of A and / or B, it is beneficial to improve the comprehensive performance of the electrochemical device, for example, the electrochemical device has a long service life, good high temperature storage performance, low temperature performance and cycle performance, etc. In the present application, low temperature refers to a temperature less than or equal to 0°C, and high temperature refers to a temperature greater than or equal to 40°C.

[0006] For example, the ratio A of the number of atoms of Mn to the total number of atoms of Ni, Co and Fe can be 3.5, 5, 10, 15, 20, 25, 30, 35, 40 or any range therebetween. Without being limited to any theory, the inventors of the present application have found that when the ratio A of the number of atoms of Mn to the total number of atoms of Ni, Co and Fe is too small (e.g., less than 3.5), the low temperature performance of the electrochemical device deteriorates, for example, the capacity retention rate at low temperatures decreases, affecting the comprehensive performance of the electrochemical device. When the ratio A of the number of atoms of Mn to the total number of atoms of Ni, Co and Fe is too large (e.g., greater than 40), manganese dissolution is prone to occur in the positive electrode sheet at high temperatures, resulting in reduced high temperature storage performance and cycle performance of the electrochemical device, shortening the service life of the electrochemical device, thereby affecting the comprehensive performance of the electrochemical device. By regulating the ratio A of the number of Mn atoms to the total number of Ni, Co and Fe atoms within the above range, the transmission efficiency of lithium ions can be improved, the manganese dissolution of the positive electrode sheet can be effectively inhibited, etc., which is beneficial to simultaneously improve the low-temperature performance, high-temperature storage performance and cycle performance of the electrochemical device, extend the service life of the electrochemical device, and thus improve the comprehensive performance of the electrochemical device.

[0007] For example, the ratio B of the number of Li atoms to the total number of Mn, Ni, Co and Fe atoms can be 0.51, 0.53, 0.55, 0.58, 0.6, 0.65, 0.7, 0.73, 0.76, 0.79 or any range therebetween. Without being limited to any theory, the inventors of the present application have found that when the ratio B of the number of Li atoms to the total number of Mn, Ni, Co and Fe atoms is too small (e.g., less than 0.51), the high temperature storage performance and cycle performance of the electrochemical device deteriorate, and the service life is shortened, thereby affecting the comprehensive performance of the electrochemical device. When the ratio B of the number of Li atoms to the total number of Mn, Ni, Co and Fe atoms is too large (e.g., greater than 0.79), the low temperature performance of the electrochemical device deteriorates, which also affects the comprehensive performance of the electrochemical device. By regulating the ratio B of the number of Li atoms to the total number of Mn, Ni, Co and Fe atoms within the above range, the transmission efficiency of lithium ions can be improved, the manganese dissolution of the positive electrode can be effectively inhibited, etc., thereby improving the low-temperature performance, high-temperature storage performance and cycle performance of the electrochemical device at the same time, extending the service life of the electrochemical device, and improving the comprehensive performance of the electrochemical device.

[0008] In some embodiments of the present application, 6≤A / B≤40. For example, the value of A / B can be 6, 10, 15, 20, 25, 30, 35, 40 or any range therebetween. Without being limited to any theory, the inventors of the present application have found that by regulating the value of A / B within the above range, it is beneficial to obtain good low temperature performance, high temperature storage performance and cycle performance, as well as a longer service life, that is, the electrochemical device has good comprehensive performance.

[0009] In some embodiments of the present application, the positive electrode plate in the aforementioned electrochemical device is assembled with lithium metal into a button cell, and in the first cycle charge capacity differential curve of the button cell, the ratio P of the area of ​​the peak between 4.4V and 4.6V to the area of ​​the peak between 3.9V and 4.6V is 0.005 to 0.2, preferably 0.05 to 0.2. For example, the value of P can be 0.005, 0.01, 0.05, 0.1, 0.15, 0.2 or any range therebetween. Without being limited to any theory, the inventors of the present application have found that when the value of P is too small (e.g., less than 0.005), the high temperature storage performance and cycle performance of the electrochemical device deteriorate. When the value of P is too large (e.g., greater than 0.2), the electrochemical device will experience a more significant deterioration in low temperature performance. By adjusting the value of P within the above range, the stability of the positive electrode active material is improved, the manganese dissolution phenomenon of the positive electrode sheet can be effectively improved, and the lithium replenishment demand of the electrochemical device during the cycle can be met, thereby improving the cycle performance and high temperature storage performance of the electrochemical device. The present application has no particular restrictions on the assembly method of the button cell, and the assembly method known in the art can be used for assembly.

[0010] In some embodiments of the present application, 0.21-0.0056A≤P≤0.2. For example, the value of P can be 0.19, 0.192, 0.194, 0.196, 0.198, 0.2, or any range therebetween. Without being limited to any theory, the inventors of the present application have found that by regulating the values ​​of A and P to satisfy the above relationship, it is beneficial to improve the high temperature cycle performance of the electrochemical device.

[0011] In some embodiments of the present application, the positive electrode sheet in the aforementioned electrochemical device is assembled with lithium metal into a button cell, and the first cycle charge and discharge efficiency E of the button cell at 2.8V to 4.6V is 90% to 110%. For example, the first cycle charge and discharge efficiency E of the button cell at 2.8V to 4.6V is 90%, 92%, 95%, 98%, 100%, 102%, 105%, 108%, 110% or any range therebetween.

[0012] In some embodiments of the present application, the Dv50 of the positive electrode active material is 8 μm to 14 μm, preferably 8 μm to 13 μm, the Dv90 of the positive electrode active material is less than or equal to 30 μm, and 1.2≤(Dv90-Dv10) / Dv50≤2.2.

[0013] For example, the Dv50 of the positive electrode active material may be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or any range therebetween. Without being limited to any theory, the inventors of the present application have found that when the Dv50 of the positive electrode active material is too small (for example, less than 8 μm), the positive electrode active material is prone to side reactions with the electrolyte, thereby affecting the high temperature storage performance and cycle performance of the electrochemical device. As the Dv50 of the positive electrode active material increases, the side reactions between the positive electrode active material and the electrolyte also decrease. However, when the Dv50 of the positive electrode active material is too large (for example, greater than 14 μm), the low temperature performance of the electrochemical device will deteriorate. By regulating the Dv50 of the positive electrode active material within the above range, it is beneficial to improve the high temperature storage performance, low temperature performance and cycle performance of the electrochemical device, and to extend the service life of the electrochemical device.

[0014] For example, the Dv90 of the positive electrode active material can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm or any range therebetween. For example, the value of (Dv90-Dv10) / Dv50 can be 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2 or any range therebetween. Without being limited to any theory, the inventors of the present application have found that by regulating the values ​​of Dv50, Dv90 and (Dv90-Dv10) / Dv50 of the positive electrode active material within the above range, it is beneficial to improve the high temperature storage performance, low temperature performance and cycle performance of the electrochemical device, as well as to extend the service life of the electrochemical device. The present application has no particular limitation on the Dv10 of the positive electrode active material, as long as it can meet the range of (Dv90-Dv10) / Dv50. For example, the Dv10 of the positive electrode active material can be 1.0μm to 17.9μm. Exemplarily, the Dv10 of the positive electrode active material can be 1.0μm, 1.4μm, 5.6μm, 11.4μm, 13.9μm, 16.0μm, 17.9μm or any range therebetween.

[0015] In some embodiments of the present application, the positive electrode active material includes spinel lithium manganese oxide (LiMn2O4) and at least one of lithium nickel cobalt manganese oxide, lithium iron phosphate (LiFePO4) or lithium-rich manganese-based materials. Without being limited to any theory, the inventors of the present application have found that by selecting the above-mentioned positive electrode active materials, it is beneficial to improve the comprehensive performance of the electrochemical device, for example, the low temperature performance, high temperature storage performance and cycle performance of the electrochemical device are improved at the same time, and the service life of the electrochemical device is extended.

[0016] The present application has no particular limitation on the preparation method of LiMn2O4, as long as the purpose of the present application can be achieved, for example, it can be synthesized by lithium carbonate and manganese dioxide at 700°C to 750°C, and the synthesis temperature is preferably 730°C.

[0017] The present application has no particular limitation on the lithium nickel cobalt manganese oxide, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to layered lithium nickel cobalt manganese oxide. Specifically, the layered lithium nickel cobalt manganese oxide conforms to the general formula Li(Ni x1 Co y1 Mn 1-x1-y1 )O2, where x1≥0, y1≥0, x1+y1≤1.

[0018] The present application has no particular restrictions on the lithium-rich manganese-based material, as long as the purpose of the present application can be achieved. For example, the lithium-rich manganese-based material conforms to the general formula Li 2-(x2+y2+z1) Ni x2 Co y2 Mn z1 O2, where x2≥0, y2≥0, z1﹥0, x2+y2+z1﹤1.

[0019] In some embodiments of the present application, the content of the positive electrode active material in the positive electrode material layer is 320 g / m 2 Up to 480g / m 2 For example, the content of positive electrode active material in the positive electrode material layer is 320 g / m 22 , 350g / m 2 , 380g / m 2 , 400g / m 2 , 420g / m 2 , 440g / m 2 , 460g / m 2 , 480g / m 2 Without being limited to any theory, the inventors of the present application have found that when the content of the positive electrode active material in the positive electrode material layer is too low (for example, less than 320 g / m 2 ), which will affect the energy density of the electrochemical device. When the content of the positive electrode active material in the positive electrode material layer is too high (for example, higher than 480 g / m 2 ), which will make it difficult for some positive electrode active materials to play their role, resulting in material waste and affecting the cost of the electrochemical device. By regulating the content of the positive electrode active material in the positive electrode material layer within the above range, it is beneficial to improve the energy density of the electrochemical device and control its cost.

[0020] In some embodiments of the present application, the electrochemical device further comprises an electrolyte, the electrolyte comprising a compound containing a sulfur-oxygen double bond, the compound containing a sulfur-oxygen double bond comprising 1,3-propane sultone and / or vinyl sulfate, and the mass percentage of the compound containing a sulfur-oxygen double bond is 0.01% to 2% based on the total mass of the electrolyte. For example, the mass percentage of the compound containing a sulfur-oxygen double bond can be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2% or any range therebetween. Without being limited to any theory, the electrolyte comprises the above-mentioned compound containing a sulfur-oxygen double bond and its mass percentage is within the above-mentioned range, which is conducive to the formation of a stable solid electrolyte interface (SEI) at the negative electrode to inhibit the side reaction between the electrolyte and the negative electrode active material, and is conducive to the formation of a stable positive electrode electrolyte interface (CEI) at the positive electrode to inhibit the phase change of the positive electrode, thereby improving the cycle performance of the electrochemical device. The positive electrode in this application may refer to the positive electrode plate, and the negative electrode may refer to the negative electrode plate.

[0021] In the present application, the positive electrode sheet may also include a positive current collector. The present application has no particular restrictions on the positive current collector, as long as the purpose of the present application can be achieved, for example, it may include but is not limited to aluminum foil, aluminum alloy foil or composite current collector, etc. In the present application, there is no particular restriction on the thickness of the positive current collector, as long as the purpose of the present application can be achieved, for example, the thickness is 8 μm to 12 μm.

[0022] In the present application, the positive electrode material layer may also include a binder. There is no particular limitation on the binder as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber or polyvinylidene fluoride.

[0023] In the present application, the positive electrode material layer may also include a conductive agent, and the present application has no particular restrictions on the conductive agent, as long as the purpose of the present application can be achieved, for example, it may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powders and / or metal fibers, and specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole.

[0024] Optionally, the positive electrode sheet may further include a conductive layer, which is located between the positive current collector and the positive electrode material layer. The present application has no particular limitation on the composition of the conductive layer, which may be a commonly used conductive layer in the art, for example, including but not limited to the above conductive agent and the above binder.

[0025] The electrochemical device of the present application may also include a negative electrode sheet. There is no particular limitation on the negative electrode sheet in the present application, as long as the purpose of the present application can be achieved. For example, the negative electrode sheet generally includes a negative electrode current collector. Among them, there is no particular limitation on the negative electrode current collector, as long as the purpose of the present application can be achieved, and it may include but is not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or composite current collector, etc. In the present application, there is no particular limitation on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, the thickness is 4μm to 12μm.

[0026] In the present application, the negative electrode plate may further include a negative electrode material layer, and the negative electrode material layer includes a negative electrode active material. The present application has no particular restrictions on the negative electrode active material, as long as the purpose of the present application can be achieved, for example, it may include but is not limited to natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 , Li-Al alloy.

[0027] In the present application, the negative electrode material layer may further include a conductive agent. The present application has no particular limitation on the conductive agent, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of the above conductive agents.

[0028] In the present application, the negative electrode material layer may further include a binder. The present application has no particular limitation on the binder, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of the above-mentioned binders.

[0029] Optionally, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. The present application has no particular limitation on the composition of the conductive layer, which may be a commonly used conductive layer in the art, and may include but is not limited to the above conductive agent and the above binder.

[0030] The electrochemical device of the present application also includes an isolating membrane. The present application has no special restrictions on the isolating membrane, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to polyethylene (PE), polypropylene (PP), polytetrafluoroethylene-based polyolefin (PO)-type membranes, polyester membranes (such as polyethylene terephthalate (PET) membranes), cellulose membranes, polyimide membranes (PI), polyamide membranes (PA), spandex, aramid membranes, woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, diaphragm paper, rolled membranes or spinning membranes. At least one of the isolating membrane of the present application may have a porous structure, and the size of the pore size is not particularly limited, as long as the purpose of the present application can be achieved. For example, the size of the pore size can be 0.01μm to 1μm. In the present application, the thickness of the isolating membrane is not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickness can be 5μm to 500μm.

[0031] For example, the isolation membrane may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, a film or a composite film having a porous structure, and the material of the substrate layer may include but is not limited to at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance.

[0032] The inorganic layer may include, but is not limited to, inorganic particles and binders. The present application has no particular restrictions on inorganic particles. For example, it may include, but is not limited to, at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The present application has no particular restrictions on binders. For example, it may include, but is not limited to, at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The polymer layer contains polymers, and the material of the polymer may include, but is not limited to, at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly (vinylidene fluoride-hexafluoropropylene).

[0033] In the present application, the electrolyte may further include a lithium salt, and the present application has no particular limitation on the lithium salt, as long as the purpose of the present application can be achieved, for example, it may include but is not limited to at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB or lithium difluoroborate. Preferably, the lithium salt includes LiPF6.

[0034] In the present application, the electrolyte may also include a non-aqueous solvent. The present application has no particular restrictions on the lithium salt non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents. The above-mentioned carbonate compounds may include but are not limited to at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds. The above-mentioned chain carbonate compounds may include but are not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or methyl ethyl carbonate (MEC). Cyclic carbonates may include but are not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound may include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The above-mentioned carboxylate compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decalactone, valerolactone, mevalonolactone, or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, cyclopentane, methyl cyclopentane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate or phosphate.

[0035] The electrochemical device of the present application is not particularly limited, and may include any device that undergoes an electrochemical reaction. In some embodiments, the electrochemical device may include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery, etc.

[0036] The preparation process of the electrochemical device is well known to those skilled in the art, and the present application has no particular limitation. For example, it may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly of a wound structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain an electrochemical device; or stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly of a stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain an electrochemical device. In addition, overcurrent protection elements, guide plates, etc. may also be placed in the packaging bag as needed to prevent pressure rise and overcharge and discharge inside the electrochemical device.

[0037] A second aspect of the present application provides an electronic device, comprising the electrochemical device in any of the aforementioned embodiments of the present application.

[0038] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0039] The present application provides an electrochemical device, which includes a positive electrode plate, the positive electrode plate includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and the elements in the positive electrode active material include Li, Mn, Ni, Co and Fe, wherein the positive electrode active material satisfies at least one of the following characteristics: (i) the ratio A of the number of Mn atoms to the total number of Ni, Co and Fe atoms is 3.5 to 40; (ii) the ratio B of the number of Li atoms to the total number of Mn, Ni, Co and Fe atoms is 0.51 to 0.79. By regulating the elements in the positive electrode active material to meet the range of A and / or B, and by regulating the elements in the positive electrode active material to meet the range of A and / or B, the obtained electrochemical device has good comprehensive performance, for example, the electrochemical device also has a long service life, good high temperature storage performance, low temperature performance and cycle performance, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present application and the technical solutions of the prior art, the following briefly introduces the drawings required for use in the embodiments and the prior art. Obviously, the drawings described below are only some embodiments of the present application.

[0041] Figure 1 This is the capacity differential curve of the button battery assembled with the positive electrode plate and lithium metal in Example 17 of the present application. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme, and advantages of the present application more clearly understood, the present application is further described in detail with reference to the embodiments below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other technical schemes obtained by ordinary technicians in the field belong to the scope of protection of the present application.

[0043] It should be noted that in the specific embodiments of the present application, a lithium-ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to a lithium-ion battery.

[0044] Example

[0045] The following examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0046] Test methods and equipment:

[0047] Test of element content:

[0048] The test method is: fully discharge the lithium-ion battery to 2.8V, disassemble it to obtain the positive electrode plate, soak it in the DMC solution for 24 hours, and then dry it for use. The treated positive electrode plate is weighed, digested, and diluted, and then the mass content of different elements is tested using an inductively coupled plasma emission spectrometer (model Thermo ICAP6300). Six positive electrode plates are tested for each embodiment or comparative example, and the average value is taken as the final result. The mass percentage of the element = the mass of the element / the mass of the positive electrode plate × 100%. Among them, the mass of the positive electrode plate is the mass after subtracting the positive current collector.

[0049] Test of charging capacity differential curve and calculation of P value:

[0050] The lithium-ion battery was fully discharged to 2.8V, disassembled to obtain the positive electrode sheet, soaked in DMC solution for 24 hours, and then dried for use. The positive electrode sheet and lithium metal were assembled into a button battery in a glove box, first charged to 4.6V at a constant current rate of 0.1C at 25°C, and then discharged to 2.8V (0.1C / 0.1C) at a rate of 0.1C. The peak area of ​​the capacity differential curve in the range of 4.4V to 4.6V during the first cycle of charging was recorded as S1, and the peak area in the range of 3.9V to 4.6V was recorded as S2, P = S1 / S2.

[0051] Figure 1 The first cycle charge capacity differential curve of the button cell assembled with the positive electrode sheet and lithium metal in Example 17 is shown. After measurement, the peak area in the range of 4.4V to 4.6V is 10.7, the peak area in the range of 3.9V to 4.6V is 100.4, and the calculated P is 0.11. The ordinate dQ / dV in the figure refers to the ratio of the difference in capacity measured twice before and after to the difference in voltage corresponding to the capacity.

[0052] Test of the first cycle charge and discharge efficiency E:

[0053] The lithium-ion battery was fully discharged to 2.8V, disassembled to obtain the positive electrode plate, soaked in DMC solution for 24 hours, and then dried for use. The positive electrode plate and lithium metal were assembled into a button cell in a glove box, first charged to 4.6V at a constant current rate of 0.1C at 25°C, then charged to 50μA at a constant voltage, and then discharged to 2.8V (0.1C / 0.1C) at a rate of 0.1C. The first cycle efficiency E = capacity at a discharge end voltage of 2.8V / capacity corresponding to a charge end voltage of 4.6V.

[0054] Test of gram capacity:

[0055] In an environment of about 25°C, the lithium-ion battery is charged at a constant current and constant voltage at a charging current of 0.5C (i.e., the current value that completely discharges the theoretical capacity within 2 hours) until the upper limit voltage is about 4.2V, and then discharged at a constant current at a discharge current of 0.2C until the final voltage is about 2.8V, and the first discharge capacity is recorded. The ratio of the first discharge capacity to the mass of the positive electrode plate is recorded as the gram capacity of the positive electrode plate. Four positive electrode plates are tested for each embodiment or comparative example, and the average value is taken as the final result. Among them, the mass of the positive electrode plate is the mass after subtracting the positive current collector.

[0056] High temperature cycle performance test:

[0057] Test the thickness of the lithium-ion battery to be tested and record it as the initial thickness. In an environment of about 45°C, charge the lithium-ion battery at a constant current and constant voltage at a charging current of 0.5C until the upper limit voltage is about 4.2V, and then discharge it at a constant current at a discharge current of 1C until the final voltage is about 2.8V, and record the discharge capacity of the first cycle as the initial discharge capacity. Then perform 500 charge and discharge cycles in the same steps, record the discharge capacity of the lithium-ion battery after 500 cycles as the cycle discharge capacity, and test the thickness of the lithium-ion battery after 500 cycles as the cycle thickness.

[0058] The cycle capacity retention rate of lithium-ion batteries at 45°C is calculated by the following formula:

[0059] 45°C 500 cycle capacity retention rate = (cycle discharge capacity / initial discharge capacity) × 100%.

[0060] The cycle expansion rate of lithium-ion batteries at 45°C is calculated by the following formula:

[0061] 45℃ 500 cycles expansion rate = (cycle thickness - initial thickness) / initial thickness × 100%

[0062] Four lithium-ion batteries were tested for each embodiment or comparative example, and the average value was taken as the final test result.

[0063] High temperature storage performance test:

[0064] The lithium-ion battery is allowed to stand for 30 minutes in an environment at 25°C, then charged to 4.2V at a constant current rate of 0.2C, then charged to 0.05C at a constant voltage of 4.2V, allowed to stand for 30 minutes, then discharged to 2.8V at a rate of 0.5C, and the discharge capacity at this time is recorded as the capacity of the lithium-ion battery before storage; then the fully charged battery is placed in an oven at about 60°C for about 7 days, and its capacity after storage is tested. The specific test process is as follows: the lithium-ion battery is allowed to stand for 30 minutes in an environment at 25°C, then charged to 4.2V at a constant current rate of 0.2C, charged to 0.05C at a constant voltage of 4.2V, allowed to stand for 30 minutes, then discharged to 2.8V at a rate of 0.5C, and the discharge capacity at this time is recorded as the capacity of the lithium-ion battery after storage.

[0065] The high temperature storage capacity retention rate of lithium-ion batteries at 60°C is calculated by the following formula:

[0066] 60°C high temperature storage capacity retention rate = capacity after storage / capacity before storage × 100%.

[0067] Four lithium-ion batteries were tested for each embodiment or comparative example, and the average value was taken as the final result.

[0068] Low temperature performance test:

[0069] The lithium-ion battery is placed in a 25°C environment for 30 minutes, then charged to 4.2V at a constant current rate of 0.2C, charged to 0.05C at a constant voltage of 4.2V, placed for 30 minutes, and then discharged to 2.8V at a rate of 0.5C. The discharge capacity at this time is recorded as the actual capacity C1 of the lithium-ion battery; then the lithium-ion battery is placed in a -10°C environment for 60 minutes, then charged to 4.2V at a constant current rate of 0.2C, charged to 0.05C at a constant voltage of 4.2V, placed for 30 minutes, and then discharged to 2.8V at a rate of 0.5C. The discharge capacity at this time is recorded as the actual capacity C2 of the lithium-ion battery. -10°C low temperature discharge capacity retention rate = C2 / C1×100%.

[0070] Example 1

[0071] <Preparation of positive electrode sheet>

[0072] The spinel lithium manganese oxide LiMn2O4 and layered nickel cobalt lithium manganese oxide Li(Ni 0.55 Co 0.15 Mn 0.30)O2 is mixed at a mass ratio of 67:33 to obtain a positive electrode active material, and then the positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride are mixed at a mass ratio of 96.5:2:1.5, and N-methylpyrrolidone (NMP) is added. The system is stirred under the action of a vacuum mixer until it becomes a uniform and transparent state to obtain a positive electrode slurry, wherein the solid content of the positive electrode slurry is 70%. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12μm, and the aluminum foil is dried at 120°C for 1h to obtain a positive electrode sheet coated with a positive electrode material layer on one side, and the content of the positive electrode active material in the positive electrode material layer is 425g / m 2 . Repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet coated with positive electrode active materials on both sides. Then, after cold pressing, cutting and slitting, it is dried under vacuum conditions at 120°C for 1h to obtain a positive electrode sheet with a specification of (74mm×867mm). Among them, LiMn2O4 is synthesized by lithium carbonate and manganese dioxide at 730°C, the mass ratio of lithium carbonate to manganese dioxide is 0.55, and the Dv50 of the positive electrode active material is 11μm and the Dv90 is 19μm.

[0073] <Preparation of negative electrode sheet>

[0074] The negative electrode active material artificial graphite, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95:2:2:1, and deionized water was added to obtain a negative electrode slurry under the action of a vacuum mixer, wherein the solid content of the negative electrode slurry was 75%. The negative electrode slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 12 μm, and the copper foil was dried at 120°C to obtain a negative electrode sheet coated with a negative electrode material layer on one side, and the content of the negative electrode active material in the positive and negative electrode material layers was 112 g / m 2 Repeat the above steps on the other surface of the aluminum foil to obtain a negative electrode sheet coated with negative electrode active materials on both sides. Then, after cold pressing, cutting, and slitting, it is dried under vacuum conditions at 120°C for 1 hour to obtain a negative electrode sheet with a specification of (76mm×869mm).

[0075] <Preparation of Electrolyte>

[0076] In a dry argon atmosphere glove box, organic solvents propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) were mixed in a mass ratio of 1:1:1, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the organic solvent to dissolve and mix evenly to obtain an electrolyte. The concentration of LiPF6 in the electrolyte was 1.15 mol / L.

[0077] <Preparation of Separator Film>

[0078] A porous polyethylene (PE) film (provided by Celgard Company) with a thickness of 7 μm and a pore size of 0.1 μm was used.

[0079] <Preparation of lithium-ion batteries>

[0080] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, and after drying, the electrolyte is injected, and a lithium-ion battery is obtained through vacuum packaging, standing, formation, degassing, trimming and other processes.

[0081] In Examples 2 to 11, except that the types and mass ratios of the positive electrode active materials are adjusted according to Table 1, the rest are the same as in Example 1.

[0082] In Examples 12 to 15, except that the mass ratios of lithium carbonate and manganese dioxide are adjusted to 0.5, 0.55, 0.57, and 0.59 in sequence so that the B value is as shown in Table 1 and the types and mass ratios of the positive electrode active materials are adjusted according to Table 1, the rest are the same as in Example 1.

[0083] In Examples 16 to 19, except that the types and mass ratios of the positive electrode active materials are adjusted according to Table 2 so that the P values ​​are as shown in Table 2, the rest are the same as in Example 13.

[0084] In Examples 20 to 23, except for adjusting the content of the positive electrode active material in the positive electrode material layer and the content of the negative electrode active material in the negative electrode material layer according to Table 3, the rest is the same as Example 13.

[0085] In Examples 24 to 28, except for adjusting the particle size of the positive electrode active material according to Table 4, the rest is the same as Example 13.

[0086] In Comparative Example 1, except that the types and mass ratios of the positive electrode active materials are adjusted according to Table 1, the rest are the same as Example 1.

[0087] In Comparative Examples 2 and 3, except for adjusting the types and mass ratios of the positive electrode active materials according to Table 2, the rest are the same as Example 13.

[0088] In Comparative Examples 4 and 5, except for adjusting the content of the positive electrode active material in the positive electrode material layer and the content of the negative electrode active material in the negative electrode material layer according to Table 3, the rest is the same as Example 13.

[0089] In Comparative Example 6, except for adjusting the particle size of the positive electrode active material according to Table 4, the rest is the same as Example 13.

[0090]

[0091]

[0092]

[0093]

[0094] Referring to Table 1, it can be seen from Examples 1 to 15 and Comparative Example 1 that when the value of the positive electrode active material A and / or B is within the scope of the present application, the comprehensive performance of the electrochemical device can be improved. For example, the electrochemical device has good low-temperature performance, high-temperature storage performance and high-temperature cycle performance, and the first-cycle charge and discharge efficiency of the button battery is significantly improved.

[0095] It can be seen from Example 12 to Example 15 that when the value of A remains unchanged, as the value of B increases, the specific capacity of the positive electrode plate shows a downward trend, and the high-temperature storage performance and high-temperature cycle performance show a gradually improving trend.

[0096] Referring to Table 2, it can be seen from Examples 13, 16 to 19, Comparative Examples 2 and 3 that when the P value is within the range of the present application, the comprehensive performance of the electrochemical device can be improved, for example, the electrochemical device simultaneously has good low temperature performance, high temperature storage performance and high temperature cycle performance.

[0097] The content of the positive electrode active material in the positive electrode material layer usually affects the comprehensive performance of the electrochemical device. Referring to Table 3, it can be seen from Examples 13, 20 to 23, Comparative Examples 4 and 5 that when the content of the positive electrode active material in the positive electrode material layer is within the range of the present application, the obtained electrochemical device has good comprehensive performance, for example, the electrochemical device has good low temperature performance, high temperature storage performance and high temperature cycle performance at the same time.

[0098] The particle size of the positive electrode active material and the relationship between the particle sizes usually affect the comprehensive performance of the electrochemical device. Referring to Table 4, it can be seen from Examples 13, 24 to 28, and Comparative Example 6 that when the values ​​of Dv50, Dv90, and Dv90-Dv10) / Dv50 of the positive electrode active material are all within the range of the present application, the obtained electrochemical device has good comprehensive performance, for example, the electrochemical device has good low temperature performance, high temperature storage performance, and high temperature cycle performance.

[0099] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrochemical device, comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode material layer, the positive electrode material layer comprising a positive electrode active material, the elements in the positive electrode active material comprising Li, Mn, Ni, Co and Fe, wherein: The positive electrode active material satisfies at least one of the following characteristics: (i) the ratio A of the number of atoms of Mn to the total number of atoms of Ni, Co and Fe is 6.7 to 40; (ii) the ratio B of the number of Li atoms to the total number of Mn, Ni, Co and Fe atoms is 0.51 to 0.68; The positive electrode active material includes lithium iron phosphate and at least two of spinel lithium manganese oxide, lithium nickel cobalt manganese oxide and lithium-rich manganese-based materials.

2. The electrochemical device according to claim 1, wherein: 6≤A / B≤40.

3. The electrochemical device according to claim 1, wherein The positive electrode plate in the electrochemical device is assembled with lithium metal into a button battery. In the first cycle charge capacity differential curve of the button battery, the ratio P of the peak area between 4.4V and 4.6V to the peak area between 3.9V and 4.6V is 0.005 to 0.

2.

4. The electrochemical device according to claim 3, wherein: 0.21-0.0056A≤P≤0.

2.

5. The electrochemical device according to claim 1, wherein the positive electrode plate in the electrochemical device is assembled with lithium metal into a button battery, and the first cycle charge and discharge efficiency E of the button battery at 2.8V to 4.6V is 90% to 110%.

6. The electrochemical device according to claim 1, wherein The Dv50 of the positive electrode active material is 8 μm to 14 μm, the Dv90 of the positive electrode active material is less than or equal to 30 μm, and 1.2≤(Dv90-Dv10) / Dv50≤2.

2.

7. The electrochemical device according to claim 1, wherein: The content of the positive electrode active material in the positive electrode material layer is 320 g / m 2 Up to 480g / m 2 .

8. The electrochemical device according to claim 1, further comprising an electrolyte, wherein the electrolyte comprises a compound containing a sulfur-oxygen double bond, wherein the compound containing a sulfur-oxygen double bond comprises 1,3-propane sultone and / or vinyl sulfate, and based on the total mass of the electrolyte, the mass percentage of the compound containing a sulfur-oxygen double bond is 0.01% to 2%.

9. An electronic device comprising the electrochemical device according to any one of claims 1 to 8.

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